Scale of acidic fog effects on epiphytes in Acadia National Park, coastal Maine

Acadia National Park is one of the remaining areas with a diverse epiphyte assemblage of macro-lichens in the Northeastern US.  Past assessments have concluded that there were no signs of negative impact of air quality on epiphytes in Acadia even though the Park experiences severe acid fog events.  We present new evidence at two scales to revisit the question of air quality effects on epiphytes in Acadia.  Water chemistry and volume of cloud water support the premise that the canopies of high elevation trees receive a higher volume of more acidic cloud water than trees at lower elevations.  At the tree-scale, maples in spruce-dominated sites had a more acid-indicating flora and fewer species in their canopies than those in deciduous-dominated sites. At the site-scale, there were no differences in overall richness.  Conifer-dominated sites were generally lower in cyano-lichens, higher in fruticose lichens, and richness was highest when hardwoods comprised 25-30% of the stand.  The pattern of more acid-indicating macro-lichen flora in tree canopies is of concern as trees in sites not influenced by acid rain generally have increasing bark pH with height on the bole and a compliment of acid-intolerant species in their canopies.  The main gradient of pollution effects is a vertical gradient on individual trees dependent on tree species, elevation and tree matrix.  Given the tree-scale occurrence of these effects, they are not detected using a site-scale assessment protocol.